The statements inside your source files are generally executed from top to bottom, in the order that they appear. Control flow statements, however, break up the flow of execution by employing decision making, looping, and branching, enabling your program to conditionally execute particular blocks of code. This section describes the decision-making statements (if-thenif-then-elseswitch), the looping statements (forwhiledo-while), and the branching statements (breakcontinuereturn) supported by the Java programming language.

The if-then Statement

The if-then statement is the most basic of all the control flow statements. It tells your program to execute a certain section of code only if a particular test evaluates to true. For example, the Bicycle class could allow the brakes to decrease the bicycle’s speed only if the bicycle is already in motion. One possible implementation of the applyBrakes method could be as follows:

void applyBrakes() {
    // the "if" clause: bicycle must be moving
    if (isMoving){ 
        // the "then" clause: decrease current speed
        currentSpeed--;
    }
}

If this test evaluates to false (meaning that the bicycle is not in motion), control jumps to the end of the if-then statement.

The if-then-else Statement

The if-then-else statement provides a secondary path of execution when an “if” clause evaluates to false. You could use an if-then-else statement in the applyBrakes method to take some action if the brakes are applied when the bicycle is not in motion. In this case, the action is to simply print an error message stating that the bicycle has already stopped.

void applyBrakes() {
    if (isMoving) {
        currentSpeed--;
    } else {
        System.err.println("The bicycle has already stopped!");
    } 
}